[PATCH] blk-mq: Make sure that the affected zone is unlocked if a request times out

[Bart Van Assche <bart.vanassche@wdc.com>]

If a request times out the .completed_request() method is not called
and the .finish_request() method is only called if RQF_ELVPRIV has
been set. Hence this patch that sets RQF_ELVPRIV and that adds a
.finish_request() method. Without this patch, if a request times out
the zone that request applies to remains locked forever and no further
writes are accepted for that zone.

Fixes: 5700f69178e9 ("mq-deadline: Introduce zone locking support")
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Ming Lei <ming.lei@redhat.com>
---
 block/mq-deadline.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index c56f211c8440..55d5b7a02d62 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -367,7 +367,8 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd)
 	 * If the request needs its target zone locked, do it.
 	 */
 	blk_req_zone_write_lock(rq);
-	rq->rq_flags |= RQF_STARTED;
+	/* Set RQF_ELVPRIV to ensure that .finish_request() gets called */
+	rq->rq_flags |= RQF_STARTED | RQF_ELVPRIV;
 	return rq;
 }
 
@@ -539,7 +540,9 @@ static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
  * For zoned block devices, write unlock the target zone of
  * completed write requests. Do this while holding the zone lock
  * spinlock so that the zone is never unlocked while deadline_fifo_request()
- * while deadline_next_request() are executing.
+ * while deadline_next_request() are executing. This function is called twice
+ * for requests that complete in a normal way and once for requests that time
+ * out.
  */
 static void dd_completed_request(struct request *rq)
 {
@@ -757,6 +760,7 @@ static struct elevator_type mq_deadline = {
 		.insert_requests	= dd_insert_requests,
 		.dispatch_request	= dd_dispatch_request,
 		.completed_request	= dd_completed_request,
+		.finish_request		= dd_completed_request,
 		.next_request		= elv_rb_latter_request,
 		.former_request		= elv_rb_former_request,
 		.bio_merge		= dd_bio_merge,
-- 
2.16.2